In a medium saucepan, blanch the green beans in rapidly boiling water for 5 minutes, or until bright green and crisp-tender.
Drain; immediately plunge into ice water.
Drain and place in a large bowl.
Add the white beans, peppers and tomatoes.
In a small bowl, whisk together the oil and lemon juice; drizzle over the vegetables.
Add the scallions, thyme and parsley; mix well.
Add salt and pepper to taste.